To study azo dye compounds preparing from the coupling reactions of diazonium salts of aniline or alkylanilines with methyl salicylate, 2-ethyl-1-hexyl salicylate or esterified cashew nut shell extract. The liquid azo dye compounds prepared from 2-ethyl-1-hexyl salicylate and esterified cashew nut shell extract were used as the novel marker dyes and subjected to qualitative and quantitative inspection both in the field test and laboratory method. The synthesized marker dyes were mixed at 1 to 5 parts-per-million concentrations in commercial diesel oil. For the field test, the marked diesel oil was extracted with suitable solvent systems comprising with ethylene glycol, methanol and bases. In the laboratory method, it was detected by visible spectroscopic technique. The marked diesel oil would be kept to observe the stability of the marker dye in diesel oil and it was found that all of marker dyes had good stability in diesel oil for at least three months.
